Molecular assays have been successfully used to perform analytical assays. Such assays can be used for detection or recognition of antibodies, antigens, analysis of nucleic acid molecules, peptide detection, drug screening, genotyping and fingerprinting, and disease diagnosis.
An assay can contain binding molecules of several disparate species of a single type or class of molecule (e.g., DNA, or protein), each species being placed on one or more points, or features, of an assay. Analytes, such as those found in a biological sample, are washed over the entire assay in a liquid medium. Analytes bind to specific features in the assay because of specific interactions between the analytes and binding molecules. Examples of such specific interactions include, but are not limited to, antibody-antigen interactions, sequence specific nucleic acid hybridization, ligand-receptor interactions, and protein-nucleic acid interactions.
When an analyte is bound to a specific feature of an assay, a fluorescent molecule acting as an optical label can often be used to indicate the presence of the analyte. The fluorescent molecule is either attached to the analyte prior to washing over the assay, or it is attached after the analyte becomes bound to the assay. In either embodiment, the result is that fluorescent molecules are localized to those areas on the assay where binding of an analyte has occurred.
Fluorescent molecules absorb light of a specific wavelength, and then emit light at a second wavelength. Detection of light of this second wavelength from an area on an assay indicates the presence of the analyte. As the volumes in the system decrease the resulting optical signals will also decrease. In a system where the instrumentation and optics of the detector are minimized, e.g., as in a handheld instrument, the problem of decreased optical signals can be compounded.
In order to increase the accuracy of detection of the optical signals in a decreased volume, it is desired to collect the fluorescent signal in a more efficient manner. Therefore, in a situation where the biochemistry of a system results in a low signal, it is desired to have a method for focusing, enhancing or amplifying the signal. The present invention collects light more efficiently from a microfluidic domain, utilizing light enhancing techniques including waveguides, light pipes and refractive index medium enhancement.